1. Field of the Invention
The present invention relates to a dynamic damper and a propeller shaft.
2. Description of the Related Art
There are dynamic dampers, which reduce vibration of an automobile driving power-transmitting member, such as a propeller shaft, in order to reduce vehicle vibration and mechanical noise. Such dynamic dampers include an outer pipe, a weight disposed inside the outer pipe and an elastic body disposed between the outer pipe and the weight. This dynamic damper is pressed into a hollow shaft constituting the propeller shaft and is fixed thereto.
In the dynamic damper disclosed in Japanese Utility Model Application Publication No. H7-29324, an elastic body is disposed in an annular space between an outer pipe and a weight, and a rod-like elastic interposed portion is provided so as to extend in the radius direction at each of a plurality of positions (five positions) in the circumferential direction of the annular space.
Conventional technology has the following problems.
(1) The elastic body is so supported that an end of each elastic interposed portion is abutted to an inner face of the outer pipe while the other end portion thereof is abutted to an outer face of the weight. For this reason, there is a concern that the elastic body may receive repeated compression in the radius direction and shearing stress in the rotation direction resulting from vibration generated when the propeller shaft is revolved, so that it may become damaged with cracks. If the weight deflects largely laterally relative to the outer pipe, or drops due to cracks in the elastic body, the dynamic damper loses its initial vibration resistant characteristic.
(2) As above-described in (1), there is a concern that the elastic body may receive repeated compression in the radius direction and shearing stress in the rotation direction based on vibration of the propeller shaft, so that it may become damaged with cracks. Thus, the dynamic damper may lose its durability.
(3) The dynamic damper must be pressed into and fixed to a hollow shaft firmly so as not to be deflected by acceleration/deceleration and vibration accompanied by a rotation of the propeller shaft. In case of a type in which the entire circumference of the outer pipe is pressed into the hollow shaft directly, both the members cannot be fitted to each other easily due to the existence of dimensional error between the inside diameter of the hollow shaft and the outside diameter of the outer pipe. Thus, a high dimensional accuracy is needed. Further, because the outer pipe is pressed into the hollow shaft with the entire circumference sliding on the inner face of the same hollow shaft, a contact area of the outer pipe relative to the inner face of the hollow shaft is increased. Therefore, a large press-in operation force is required, which leads to an increase of cost for production equipment.